Note: Descriptions are shown in the official language in which they were submitted.
7~ c
W. R. GRACE & CO.
GJ E 6 O 8 1 / 6 8
SEALING COI'~POSlTIONS
This invention relates to sealing compositions
-intended for sealing container closures such as top or
bottom end closures of cans or replaceable or non-replace-
able caps for jars or bottles. The compositions can also
be used for other sealing purposes but, for clarity,
since~they are formulated to meet the particular require-
ments of can and other container closure seals the
invention is described solely in terms of compositions
for seal;ng container closures.
Traditional container end sealing compositions
have comprised a liquid medium in which has been dispersed
or dissolved rubber or other polymeric material and
which includes also fillers, tackifying resin and other
additives.
The liquid medium may be aqueous, for instance
as in US Patent Specificat;on No. 3,409,567 or British
Paten~ Specification No. 1566924, or the liquid medium
may be organic, for instance as in British Patent
Specification No. 1,340,730. A wide variety of fillers
have been proposed for use in the compositions, for
instance as is shown by these patent specifications, but
only a few have proved to be satisfactory in use.
Typical fillers that have been found satis-
factory include kaolin, talc, zinc oxide and calcium
carbonate. Generally the amount of filler must not be
too high or else the sealing properties are impaired.
The liquid composition is applied to one at
,; ~ least of the mating surfaces of the closurc and the
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sealing face of the conta;ner, generally to the closure,
and is then ~ried on the surface. The closure is
pressed onto thc sea]ing face oI the container so as to
grip the container firmly and the composition provides a
S seal between the container and the closure.
It is necessary that the composition should
have appropriate rheological and other physical properties.
For instance when applied to can ends it should flow
adequately during sealing so as to distribute itself
over the mating surfaces, but preferably it does not
flow to such an extent that significant extrusion of
the composition occurs along the walls of the can. The
seal provided by the composition should prevent ingress
of bacteria. Generally it should also prevent loss
of liquid, vacuum or gas.
It has been our object to provide sealing
compositions that satisfactorily seal container
closures and that include filler that has not previously
been proposed for this purpose, Preferably the filler
2~ is such that, compared to use of fillers commonly used
at present, either the seal is improved or the amounts
of either the rubber or other polymeric material or the
tackifying resin, or both, can be reduced without
reducing the sealing properties. It has also been our
object to provide methods of sealing containers using
such compositions, and to provide sealed containers.
A sealed container according to the invention
has a closure sealed to it by a seal that includes a
gasket formed of a rubbery polymer in which is dispersed
filler including crush resistant metal part;cles having a
particle size of less than 200 microns.
A novel composition according to the invention
comprises a rubbery polymer and filler that is clispersed
throughout the composition and that includes the particles
and generally also tackifying resin. The composition
may be a meltable solid but preferably comprises also
a liquid medium in which the polymer is dissolved or
dispersed.
~- The sealed container may be fully sealed, for
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instance b~ing a jar or a one piece can or a can sealed
at both ends, or it may be a can that has a closure
sealed to it one end but wh;ch is open at the other.
Such a sealed container can be formed from
5 a container and a container closure in conventional
manner. Thus the sea]ing face of the closure is lined
with a liquid composit;on comprising rubbery polymer
and a dispersion of the filler, the composition is
solidified (generally by drying) to form a gasket, and
the sealing ace of the closure is compressed around
the end of the container thereby sealing the closure
to the sealing face with the gasket within the seal.
When the container is a bottle this gasket i$
trapped between the sealing face of the rim of the
bottle and the overlying closure. Preferably however
the container is a can in which event the gasket is
I trapped in the double seam formed in conventional manner
! by compressing the outer periphery of the container
closure around an outwardly extending flange of the side
wall and then pressing the flange and the closure
periphery against the side wall of the container generally
in a single operation.
The particles must be crush resistant, that i~
to say they must have sufficient strength to resist any
risk of crushing during the sealing use to which the
composition is to be subjected. Thus in a can end
sealing composition the beads must have sufficient
strength that they will not crush in the seal. In order
that they are crush resistant the particles must be formeclof
a hard metal. Thus a soft metal such as tin is
unsatisfactory but hard metals such as stainless steel,
nickel alloy or chromium are satisfactory.
The particles may have a rough surface or a smooth
surface and may have a regular shape or an irregular
shape. Preferably however any roughness or irregularity
is not too extensive since otherwise this may increase
the adhesion of the rubbery polymer to the surface of
the particles to such an extent to deminish the advantages
i, ~ ..
that are otherwise obtained. Preferably the particles
are substantially smooth.
The particle size range of the beads is
generally between 1 and 100 microns, preferably 10 to
75 microns, The maximum particle size most preferably
is not more than 60 microns. The average particle
size is generally from 5 to 100 microns, most preferably
10 to 50 microns, with best results generally being
achieved with an average size of 20 to 50 microns.
The metal particles may have been given a
surface coating of a variety of materials provided the
surface coating does not interact with other components
in the composition in such a way as to reduce
significantly the sealing properties of the composition.
lS Throughout this specification amounts of
components of the composition, including amounts of
metal particles and other fillers, are expressed as
amounts by volume based on the volume of rubbery polymer,
unless otherwise specified. For instance 10~ particies
means 10 volumes particles per 100 volumes rubbery
polymer.
The amount of the particles in the
composition should be at least 1%, since lower amounts
tend to give inadequate improvement. Generally the
amount is below 150~o ~ and normally below 100~, since
greater amounts tend not to give significant further
improvement. Generally the amount is at least 3~,
and normally, at least 5~. Preferably the amount is
at least 10~. Generally the amount is up to 50~.
Typically the amount may be from 5 to lOO~o ~ most
preferably 10 to 50~.
The filler may consist substantially only
of the particles, with the result that the composition
may contain no significant amounts of other fillers,
although it may include fillers that are present
primarily for their pigmentary purposes, for instance
titanium dioxide which may be present in amounts of up
to 10 or 15~,
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Good results are also obtained when the
filler does include other particulate inorganic material
and this is generally preferred. The material other
than the particles may be present in an amount of 0 to 150~o
(based on the volume of rubbery polymer), generally 10
to 100% and preferably 15 to 100~. Preferably the
composition includes 0.05 to 2 parts, most preferably
0.1 to 1 part, by volume particles per part by volume
other inorganic particulate filler.
Although the total volume of filler, including
the particles, can be similar to that conventionally
used in commercial sealing compositions, for instance
10 to 45~, a particular advantage of the invention is
that larger amounts of total filler may be used while
still obtaining satisfactory sealing properties. For
instance the total amount of filler, including the
particles, is usually at least 20~ ~by volume based
on the volume of rubbery polymer) and can be up to 175~,
for ins.ance 50 to 125~.
Titanium dioxide or other pigmentary filler
(for instance carbon black) generally has a particle
size below 5 microns but other particulate inorganic
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~ ~ o~
fillers that may be used in the invention generally have
a particle size of from 1 to 50 microns. The -filler
should be subs~antially non-abrasive, so that it does
not cause wear to the machinery by which the composition
is mixed and li~ed onto the can or other end.
The preferred other filler is kaolin or china
clay or zinc oxide but other fi]lers inc]ude co]loidal
silica and other silicic fil]ers, synthetic silicate,
calcium carbonate or sulph~te, a3uminium hydroxide,
talc, dolomite, barium s~ phate, or magnesium oxide or
carbonate or silicate. Such fillers may have been
surface treated, for instance in conventional manner. ..
Instead of modi~ying the colour of the
composition by including particulate pigment some other
15 colouring material, for instance a soluble dye, may be
included.
The composition is formed from a rubbery
polymer, that is to say a polymer that, when dried,
forms a gasket that is sufficiently flexible and
20 resistant to be capable of serving as a seal. It
should have the conventional properties of rubbery
polymers, i.e. it should be capable of being subjected
to substantial reversible deformation, Rubbery polymers
suitable for forming seals are well known. Generally
the Mooney viscosity (ML104 C) of the rubbery polymer is
from 20 to 200, preferably 40 to 160.
The rubbery polymer may be a natural polymer,
for instance natural rubber, or may be a synthetic polymer.
30 Suitable synthetic rubbery polymers include butyl rubber,
polychloroprene, butadiene acrylonitrile copolymers,
ethylene propylene copolymers, ethylene-propy3ene-diene
terpolymers, styrene isoprene block copolymers, poly-
butadiene, styrene acrylic copolymers, polyvinyl;dene
35 chloride, polyvinylidene chloride copolymers, plasticised
polyvinyl chloride, polyvinyl chloride copolymers,
plasticised polyvinyl propionate or acetate~ polyvinyl
propionate or acetate copolymers, polyacrylic acid
copolymers, polymethylacrylic acid copolymers, acrylic
~ t~3
ester copoly~pel-s, methacr~rlic ester copol~ers,
plasticised pol~styrene, vinyl acetate copol~mers
;ith for instance ethylene, styr~ne butadiene block
copol~-mers, styr~ne butadiene rubbers solùtion polymer-
ised or emulsion polymerised, and carboxylated st~renebutadiene copolymers. Blends may be used.
~ Compositions based on vulcanisable polymers may include
; vulcanising agent.
Naturally the rubbery polymer will be chosen
having regard to, for instance, the type of composition
that is being used for forming the seal. The preferred
polymers are styrene butadiene rubbers having a styrene
content of 15 to 60~ preferably 18 to 45~ by weight.
They may have been made by any convenient polymerisation
method, and thus may have been made by hot or cold
polymerisation techniques.
Tackifier resins are generally included in
can sealing compositions and they may be included in
~he compositions used in the invention. However
~0 because of the good sealing properties obtained
by the use of novel filler satisfactory results can
often be obtained without a tackifier resin in the
invention. Instead of using a tackifier resin a
liquid plasticiser, such as white oil or other hydro-
carbon oil, that softens the polymer may be used in amountsof for instance 1 to 60%, preferably 5 to 40~
Best results are generally obtained when
tackifier resin is included. Suitab~e materials are
well known and are generally selected from synthetic
hydrocarbon or petroleum resins, polyterpene resins,
phenolic resin modified with natural resins such as
rosin or terpene, xylene formaldehyde resin and modified
products thereof, and esterified rosins or otller rosin
type resins such as rosin, hydrogenated rosin, or
hardened rosin. The amount of tac~ifier is generally
at least 10~ ~by volume of rubbery polymer) but less
than 250~ and preferably less than 200~. Generally
the amount is at least 15~.
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8 l
The compositions may include minor amounts,
e.g. up to 1~ or at most up to 5-0 of other additives
that are ~nown to those skilled in the art and that are
conventional in filled sealing compositions, such as
viscosity increasing agents (for instance aJ~onium
alginate, bentonite or gum karaya or high Molecular
~eight polyacrylic acid), bactericides, corrosion
; inhibitors, surfactants, anti-oxidants (for instance
phenolic or amino anti-oxidants) and p~-l adjusters (for
instance ammonia~ primary amine, sodium hydroxide or
sodium carbonate~.
The composition preferably is liquid at
room temperature and thus preferably includes a liqùid.
medium that serves as a carrier for the rubbery polymer
and the filler.
The amount of the liquid medium will be
chosen having regard to the maximum total solids
concentration obtainable in the final composition
consistent with solubility or dispersibility of the
polymer in the liquid medium, ease in preparing the
composition, storage stability of the composition,
and application of the composition to the can end
using high speed automatic lining equipment. In general, - ~
the amount of liquid medium is such as to yield a .
composition having a solids content of from 20% to 85
by weight.
Preferably the liquid medium is aqueous~
The aqueous composition will generally contain at
least one stabiliser for stabilising the dispersion.
This stabiliser may be selected from any of the
materials conventionally used for stabilising aqueous
sealing compositions based on filler and rubbery
polymer. Such stabilisers include styrene maleic
anhydride or other styrene copolymers, methyl cellulose,
polyacrylamide, ethoxylated condensates, polyvinyl
pyrrolidone ammonium oleate, and casein. Such
stabilisers may be used in admixture, for instance
with other materials.
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The aque~us composition is pre~er~bly a
late~ obtained by dispersing the specified fil]er and
tac~ifier (if present) into a latex of the chosen
rubbery polymer, for instance as formed by emulsion
polymerisation, ~he composition may be made simply
; by mixing into the chosen latex ~optionally after dilution)
the tackifying resin, the se]ected fil]er or fillers,
and any other additives, all in convc-ntional manner.
Naturally care must be taken to ensure that the latex
does not coagulate and that a uniform dispersion is
obtained. For instance it may be desirable to form a
dispersion of the iller or fillers, and optionally
also tac~ifier, and add this stable dispersion to the .
latex. The total solids content of the composition
is generally from 20 to 85~ by weight, prëferably 30
to 80~.
Instead of formulating the aqueous composition
as a latex it may be a dispersion obtained by dispersing
solid rubbery pol~mer and filler into the aqueous medium.
The aqueous dispersion may be made by mill ing the solid
rubber with filler and other optional additives, including
also generally any tackifying resin, using an internal
mixer, for instance a ~anbury mixer, so as to form a
rubbeT stock. This rubber stock is then dispersed
in water in conventional manner, for instance using a
Z-blade type of mixer. Additional components, for
instance thickening agent and more water, may be added
to the dispersion to alter its consistency. Instead
of including all the major additives in the rubber stock
some may be added to the dispersion, For instance the
rubber may be milled with some of the additives and
then dispersed in water and other major additives
introduced at this stage. For instance the novel filler
of the invention may be added to the aqueous dispersion
35 obtained by dispersing solid rubber and optionally some
of the filler.
Although aqueous compositions are preferred
the compositionS of the invention can be organic, in
,
~;hich the liquid medium comprises organic solvent in
~hich some or all o~ the rubbery polymer will dissol~e,
any remaining polymer going into dispersion.
Suitable organic liquids ~Ihich may be employed
in preparing organic compositions include aliphatic
and aromatic hydrocarbons, for example 3-methylheptane,
hexane, heptane, xylene and toluene; chlorinated
hydrocarbons, such as dichloropentane; ketones; ethers,
ether-alcohols and mixtures of these and other volatile
organic liquids which together form media as known in
the art for the selected elastomers.
The organic compositions are generally made
by blending the solid rubber with filler and optional
additives such as anti-oxidants in an internal mixer,
for instance a Banbury mixer. The solid rubber stock
j thus obtained is comminuted and dissolved in the
¦ chosen solvent or solvent mixture in conventional manner.
If tackifying resin is to be introduced it may be added
to the solvent or it may be blended into the solid
rubber stock.
The composition may be an organosol of the
rubbery polymer, filler, plasticiser, organic solvent - -
and other optional additives.
The composition may be a melt consisting of
the rubbery polymer and ~iller, and other optional
additives. For instance the novel filler of the
invention, and optionally other filler, may be mixed
into the polymer while it is soft and the mass then
fully melted before application to the closure.
We find that the inclusion oE the metal particles
does, as a ~enerality, result in improved sealing
properties compared to the same composition in wh;ch an
equivalent volume of other filler (such as kaolin) is
used in place of the metal particles.
A number of sealing tests are used in the
industry and are recognised as being meaningful and
by saying that the sealing properties are improved we
mean that the number of cans that fail a meaningful
sealing test will be red~1ced. In some instances there
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may be no improvement in the results of some sealing
tests but improvements in other tests wi]l sho\~ that,
despite this, there is a useful practical impro~ement.
Metal partieles also have the advantage that they
can have inert surface characteristics and so can
avoid some of the handling and other difficulties
that may be encountered with other -fillers. For
instance fillers such as calcium carbonate~
~ - can lead to a
risk of coagulation of a polymer latex into which such a
filler is incorporated. Accordingly when such fillers
are used it is necessary to take particular precautions
to prevent coagulation of any latex or dispersion that ,
is present.
The most consistently satisfactory sealing
properties and the greatest tendency for a significant
improvement in sealing propertie~ is obtainable in
the invention when the metal particles are included in
aqueous compositions, and especially in latex compositions,
and so these are preferred.
Some non-limiting examples of the in-veJl-tion
are now given.
In these sealing properties are identified by
two sets of quantitative values which are referred to
- 25 as "biological seal" and "sterilisation extrusion".
These are recorded as follows~
"Biological Seal" The composition is
_
lined into can closures (often termed can ends) and
dried in conventional manner, the amount of the
composition being such as to give the dry film volume
generally recommended for the particular size. Cans
having a soldered side seam are then filled with a hot
liquid nutrient, typically at a temperature of 97C,
leaving a small headspace. The test closures are double
seamed onto these filled cans whilst simultaneously
injecting steam into the headspace. The closed cans
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are th~n sterilised, ~ypically at ~21C for 30 mi~utes,
and after sterili~at;on are immediatel~ cooled in .ater
containing ~as-producing, non-pathogenic micro-organisms
capable of growth in the aforementioned nutrient. After
cooling and whilst still wet with the cooling ~:ater, the
cans are subjected to a controlled deformation at the
junction of the side seam and the double seam of the
test closure. After incubation for six days at an
elevated temperature optimum for the growth of the
micro-organisms, followed by one day at ambient
temperature, the cans are examined visually and the
number of swollen cans recorded. The retained vacuum
in the remaining cans is measured. Cans having a
low retained vacuum and the swollen cans are considered
to have reached this condition through failure of the
seal in the test closure, The swollen and low vacuum
cans are termed failures and the "biological seal"
value is the failure rate expressed as the number of
such cans per thousand tested. Because of the
procedures used the number of failed cans per thol-~and
in this biological seal test is of course ~ery much
greater than that which would occur with commercially - ¦
packed cans sealed with these compositions. -
"Ster isation extrusion". The composition is
lined into can closures and dried, in conventional
manner, the amount of the composition being such as to
give a dry film volume approximately 20~ greater than
that generally recommended with the particular closure
size. Cans ara filled with water at typically 70C
to leave no headspace and test closures are double scamed
onto these filled cans. The closed cans are then
sterilised typically at 130C for one hour and allowed
to cool to room temperature before examination. The
number of protrusions of coMpound from the double seam
along the outside wall of the can body at the test
closure is counted, typically on a sample of 10 cans
for each composition. Large protrusions are counted
as appropriate multiples of the typical, more commonly
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occurring, small protrusions The average numl~er of
protrusions per can is recorded as the value for
"extrusion", This value should be as low as possible,
preferably below 10 under the conditions of the test.
Ho~ever, because of the extreme conditions of the test,
greater values than this are commercially tolerable.
Since the extrusion and biological seal resu]ts
will vary according to, for instance, variable
conditions under which the tests are carried out compari-
sons should, in general, be made only between resultswithin a single example. It is desirable that the
"biological seal" and "sterilisation extrusion" values
should be as low as possible.
In the following examples each composition is
made by mixing together a latex of a rubbery polymer
and containing minor amounts of conventional additives
known to those skilled in the art, stabiliser, filler,
titanium dioxide pigment, and tackifier resin. The
composition is lined onto the can closure, dried, and
tested in the described manner.
The amount of tackifier resin is 22%, the
amount of stabiliser is 4.2% and the amount of titanium
dioxide is 3.2%, all based on the volume of rubbery
polymer in the latex. The amount of filler is given
in the examples by volume based on the rubbery polymer.
When the filler is kaolin the total solids content of ~~~~
the composition is about 60% by volume.
The filler consists of metal particles (if
present) and the stated inorganic particulate material (if
present) which generally has a particle size of 1 to 50
microns although titanium dioxide may have a particle size
of down to 0.1 microns.
The latex is a styrene butadiene latex hav;ng
a solids content of 66 to 69% by weight and containing
31 to 36% bound styrene and which has been polymerised
cold (at 5C) using fatty acid soaps. The polymer in
the latex has a Mooney value (as defined above~ of 100
to 130. I~owever, similar results may be obtained using
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14 ~
other styrene butadiene latices that may have' been
polymerised hot or cold such as those listed in the
following table:
Type Total Solids Bound Mooney Emulsifier
~ ~~~ ~ Styrene ~D Value
Cold 63 29 140 Fatty acid
Cold 67 34 75 Fatty acid
Cold 68 30 150 Fatty acid
Hot 45 46 90 Rosin ester
}lot 42 50 30 Rosin ester
Hot 59 46 75 Rosin ester
Hot 50 46 70 Rosin ester
The tackifier resin is a polymer of mixed
5-carbon alkenes having a melti~g point of about 100C.'
The stabiliser is a styrene-maleic anhydride copolymer.
Similar results are obtainable with other tackifiers
and stabilisers.
Exam~le 1
Test Filler ¦Biological Sterilisation
l~al- __ Extrusion
.
lA 30 Kaolin 250 26.4
lB 30 Spherical Tin Beads240 22.8
(4 to 60 microns~
lC 30 Nickel Alloy spheres15 8.2
(50 microns mean diameter~
lD 30 Nidel spheres having120 0.0
smooth surface
(2 to 40 microns)
lE 30 Nickel spheres having70 0.0
rough surface
(3 to 30 microns~
lF 30 Chromium irregular shaped 95 17.7
beads ~50 to 75 microns)
lG 30 Chromium irregular beads 35 0.0
(2 to 40 microns)
$ ~
t~$~
Example 2
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~ __ ._ __ _
Test Filler B~ogical Sterilisa-
Seal tion
Extrusion
_ ..
2A 30 Kaolin 825 16.0
2B 30 Stainless Steel 285 0.1
spheres ~0 to 60
microns)
.__ _ _
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